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A tri-color Michelson-type spatial phase-shift digital shearography is introduced to measure three displacement gradients, including one out-of-plane component and two in-plane components, simultaneously. By using this setup, three shearograms are recorded simultaneously in a single frame. The high-frequency components of these shearograms are then separated in the frequency domain due to their different spatial frequencies which are produced by the use of three lasers with different wavelength, yielding three individual phase maps with which the three displacement gradients are solved. The detailed capability of the proposed approach is described by theoretical discussion as well as experimental demonstration. [ABSTRACT FROM AUTHOR]

A temporal 4-step polarization phase-shifting technique for digital speckle pattern interferometry (DSPI) with one fixed and two rotatable polarizers is proposed. The fixed polarizer is used to filter out the reflected object beam in one polarization direction, and the two rotatable polarizers are used to perform the 4 times phase shifts. The Jones derivation illustrates the object surface phase distribution can be derived from the 4 speckle pattern interferograms, which are bright, gloomy, bright, and gloomy successively. The experiment shows that the proposed temporal polarization phase-shifting technique is able to extract the phase change caused by a tiny out-of-plane displacement. Unlike the PZT-driven phase-shifting, the polarization phase-shifting in this method is stable and accurate in the long term. [ABSTRACT FROM AUTHOR]

This paper presents a simple spatial phase shift shearography based on the Michelson interferometer. A novel digital shearography set-up with a large angle of view, which is based on a 4 f system is demonstrated. In the system, the Michelson interferometer is used as a shearing device to generate a shearing distance by tilting a small angle in one of the two mirrors. In fact spherical wave fronts become plane after going through the first lens in 4 f system. Tilting the mirror in the Michelson interferometer also generates spatial carrier frequency. Sinusoid fitting method is applied to evaluate the phase. This system can generate a phase map of shearography by using only a single image. The effects of shearing angle, the choice of algorithm and comparison result are discussed in detail. The theory and the application are presented. [ABSTRACT FROM AUTHOR]

Digital shearography has become a competitive tool for vibration analysis due to its capability of full-field, high resolution, and high-speed measurements. Many stroboscopic shearographic systems have been developed in recent years. However, they are only suitable for vibration analysis of a small area. This paper presents a shearographic system that was developed to carry out the vibration analysis of a large-area object whose area is 1 m or even bigger. The system can use both time-average and stroboscopic illumination methods to analyze the forced vibration distribution. The setup of the system is introduced and experimental results are presented. [ABSTRACT FROM AUTHOR]